Not only T-Mobile. There's a new race of crypo adoption and Amazon, Line, Telegram, A russian state bank are all taking part in this race. This indeed would be good for crypto in the short term, but I wonder, what happens if these powerhouses are able to control a large share of the "decentralized" market and influence it. Much like how it is rumored to be true in the case of Bitmain.
T-Mobile are not going to enter the cryptocurrency market because they simply have no reason to do that, the blockchain has nothing to do with Mobile networks.
About Amazon, I wouldn't say that accepting bitcoin would mean that they support it, all it means that they want to create buzz and to attract more people.
Anyway, as far as I know, when amazon accepts bitcoin they are going to use BitPay, which means that they don't really believe in bitcoin and they are not going to keep it, it's the same as accepting fiat payments from their side.